Lamb: remove lamb from packaging and pat dry with paper towel. The set side.
Dry rub: in a glass combine mustard powder, garlic powder, onion powder, paprika, salt and pepper. Stir with a mini whisk to combine.
Season lamb: place lamb shoulder on chopping board and massage dry rub into top side. Flip and repeat for the underside.
Liquids: combine Worcestershire sauce and apple cider vinegar in a glass jug, stir to mix together.
Slow cooker: pour combined liquids into the base of the slow cooker. Place seasoned lamb on top, pop the lid on and cook for 4 hours on high or 8 hours on low.
Sauce and grill: once the cook time is up, lift the lid off the slow cooker and turn the dial to off. Use a pair of kitchen tongs to lift the cooked lamb up and out of the bowl. Place this directly onto a silicon lined baking rack. Use a pastry brush to gently but liberally coat the lamb with the BBQ sauce.
Grill/broil: preheat the oven setting to grill at 200°C 392°F6. Place the baking rack into the oven on the top shelf. Grill the lamb for 10 mins (no need to flip). Repeat basting process followed by a further 10 mins grill time.
Pull: once the lamb has been grilled use 2 pairs of kitchen tongs (1 in each hand) to transfer it to a chopping board. Then use a knife to make a few initial cuts and remove the bone from the lamb. Next use a fork in each hand and a pulling (widening of your 2 hands) to shred the lamb.
Serve: use the pulled lamb to fill burger buns, make sliders, add to salad or make soft shelled tacos.